The formation of dental plaque involves the sequential colonization of oral bacteria on the saliva coated tooth surface. The primary colonizers, which include the sanguis group streptococcal species, S. gordonii and S. sanguis, create a substratum to which later-colonizing species, including pathogens can attach. As a result, the sanguis group streptococci not only influence the composition of mature dental plaque, but also the balance of a healthy or diseased oral environment. Although S. gordonii and S. sanguis are primarily commensal members of the oral cavity, physical dispersion as a result of dental treatment allows them to disseminate via the bloodstream to colonize heart valves and cause infective endocarditis, one of the few potentially lethal complications of dental treatment. Previous taxonomic classification and more recent molecular based studies indicate a high level of diversity among the sanguis group. The recent availability of the S. gordonii strain Challis and S. sanguis strain SK36 genome sequences and development of genomic based tools for large-scale genomic comparisons now allows for a genome wide examination of multiple isolates. The goal of this discovery-driven R21 project is to examine the genomic repertoire of oral and endocarditis isolates from these species using DNA microarray based approaches for gene discovery and diversity. The specific aims are: 1) Using representatives of each of the three S. gordonii biovars, construct whole genome shotgun library comparative genome hybridization (SL-CGH) gene discovery DNA microarrays which will identify genes and genomic regions not present in the sequenced S. gordonii strain Challis genome and 2) Construct comprehensive 70-mer oligonucleotide S. gordonii and S. sanguis DNA microarrays and use them to examine the genomes of representative S. gordonii and S. sanguis oral, blood and infective endocarditis clinical isolates to identify genome diversity within this species. Analysis of these data will provide information on the genomic diversity of the S. gordonii and S. sanguis species and provide insights into the biology of the organisms. The microarray tools developed, which will have genes representative of a variety of strains of each species, will be of use to the entire streptococcal community. The newly available data will provide the basis for functional genomic studies to understand the biology of these organisms. [unreadable] [unreadable] Public Health: The objectives of this proposal are to measure the level of genetic diversity among the sanguis group oral streptococci and determine if this diversity selects for specific isolates capable of causing infective endocarditis. [unreadable] [unreadable] [unreadable]